1. Field of the Invention
The present invention relates to a system and method for controlling fuel injection of a common rail fuel system in a multi-cylinder internal combustion engine.
2. Background Art
Common rail fuel systems are used in various types of internal combustion engines, such as diesel engines, for example. An accumulator or rail is used to distribute fuel to injectors or nozzles associated with each cylinder of the engine. An engine control module communicates with various engine components including one or more fuel pumps and fuel injectors to meter the fuel delivered to each cylinder, i.e. control the quantity and timing of the fuel delivery to ultimately control the performance and emissions of the engine.
A number of strategies have been developed to control fuel injection in an attempt to improve engine performance and fuel economy while reducing emissions. One such strategy employs multiple fuel injections during a single combustion cycle. Depending upon the particular application and operating conditions, the fuel injection for a single combustion cycle may be split into a pilot injection, a main injection, and one or more post injections, for example. The quantity and timing of each injection should be accurately controlled to achieve the intended benefits of using multiple injections, particularly for the pilot and post injections because of their relatively smaller volumes and short durations. However, many factors affect the injection events, such as common rail fuel pressure and injector energizing time, for example, making this a difficult task to accomplish. One prior art control strategy used for conventional fuel systems employing electronic unit injectors (EUIs) determines the beginning of injection for the main injection based on the-beginning of injection time and the duration of the pilot injection. While this strategy is acceptable for conventional EUI systems, for a common rail system the durations of the pilot and post injections are a function of the fuel pressure within the common rail and are therefore difficult to accurately control.
The present inventors have recognized various shortcomings of the prior art approaches and have developed a system and method for controlling multiple fuel injections for common rail fuel systems that is believed to provide more accurate control, particularly during transient operating conditions, which may contribute to improved engine performance and fuel economy while reducing emissions.